1. Field of the Invention
The present invention relates to a method, system, and computer program product for detecting a type of NAT (Network Address Translators) Firewall by utilizing SIP messages.
2. Description of the Related Art
RFC 3489 defines Simple Traversal of User Datagram Protocol through Network Address Translators (NATs) (STUN), which is a collection of methods, including a network protocol, used in NAT traversal for applications of real-time voice, video, messaging, and other interactive IP communications. The STUN protocol allows applications operating through a NAT to discover the presence of a NAT and to obtain the mapped (public) IP address (NAT address) and port number that the NAT has allocated for the application's User Datagram Protocol (UDP) connections to remote hosts. The protocol requires assistance from a 3rd-party network server (STUN server) located on the opposing (public) side of the NAT, usually the public Internet. The original version of the protocol also specified methods to ascertain the specific type of NAT, but those methods have been deprecated in the newer specification (RFC 5389), because of the plethora of specific NAT implementation behavior in various networking equipment and the resulting intractability of the problem and the deficiencies of the method used the original specification. As a result, a need arises for a technique by which a NAT type can be successfully determined and which does not require the use of special hardware.